Add Iterable.intersperse extension method

CHANGELOG.md

@@ -1,6 +1,6 @@
 ## 1.19.0-wip
 
-- Adds `shuffled` to `IterableExtension`.
+- Add `Iterable.shuffled` and `Iterable.intersperse` extension methods.
 - Shuffle `IterableExtension.sample` results.
 
 ## 1.18.0

lib/src/iterable_extensions.dart

@@ -601,6 +601,21 @@ extension IterableExtension<T> on Iterable<T> {
       yield slice;
     }
   }
+
+  /// Insert a specific element between each two elements of this iterator.
+  ///
+  /// For example, `[1, 2, 3].intersperse(0)` returns `(1, 0, 2, 0, 3)`.
+  Iterable<T> intersperse(T element) sync* {
+    var first = true;
+    for (final e in this) {
+      if (first) {
+        first = false;
+      } else {
+        yield element;
+      }
+      yield e;
+    }
+  }
 }
 
 /// Extensions that apply to iterables with a nullable element type.

test/extensions_test.dart

@@ -1262,6 +1262,23 @@ void main() {
         expect(l3.toList(), [4, 5]);
       });
     });
+    group('.intersperse', () {
+      test('empty', () {
+        expect(iterable(<int>[]).intersperse(0), []);
+      });
+      test('one element', () {
+        expect(iterable(<int>[1]).intersperse(0), [1]);
+      });
+      test('two elements', () {
+        expect(iterable(<int>[1, 2]).intersperse(0), [1, 0, 2]);
+      });
+      test('more elements', () {
+        expect(
+          iterable(<int>[1, 2, 3, 4]).intersperse(0),
+          [1, 0, 2, 0, 3, 0, 4],
+        );
+      });
+    });
   });
 
   group('Comparator', () {